Apparently, only a very small fraction of the cases, if every instance of a wreck being left behind marks a successful ejection.
Clearly, ejecting while the ship still remains undestroyed is a dangerous operation: if any of this potent Star Trek antimatter is spilled in the process, the crew will die anyway. So the ejection system probably never will save lives aboard the doomed ship. But it will
save lives aboard ships next to that one!